The present invention relates to equipment for moulding products from a pre-heated parison of thermoplastics material, comprising at least two mould sections having one or more mould elements, where the sections are positionable to encompass the parison to shape and cool the parison. Each mould section is supported by a reciprocating carrier part and further comprises a cooling circuit for cooling the mould section, and a network of channels/bores that conducts gas (air) to/from orifices arranged in the mould section. The invention also relates to the use of the equipment in a blow-moulding apparatus.
Equipment of this type is particularly suitable for moulding hollow products, where a hollow parison is formed by an extrusion head in which a blow pin supplies pressurized gas (air) to the parison to expand it into conformity with the walls of the cavity formed by the interior of the closed mould sections.
GB Patent Specification No. 1,560,423 relates to apparatus for moulding extruded parisons. The apparatus comprises an extrusion head that forms a parison and brings it to a moulding zone where two reciprocating mould sections are adapted to encompass the parison. The mould sections are supported by two reciprocating carrier parts, the movement thereof being controlled according to a moulding cycle. This state of the art equipment may further comprise mould sections having a base part with mould elements inserted or shaped in the base part and a cooling circuit together with a network of channels/bores to conduct air to/from orifices arranged in conjunction with the mould elements. The cooling circuit and the network for air are connected to external systems by means of connectors provided in the base part. The cooling circuit comprises a system of channels/bores in both the base part and the mould elements, enforcing the use of seals or O-rings between removable mould elements and the base part.
As the above mentioned mould sections are removed out of the apparatus in connection with maintenance work or a change of moulds, the cooling circuit has to be opened. This implies that the connectors have to be detached, and coolant liquid will leak out of the circuit, causing a spill on the floor. Furthermore, as the mould sections are quite heavy, hoisting equipment is required when performing such operations. The following mounting operation has to be performed with a high degree of accuracy to obtain a correct position of the mould sections.
Mould elements that are removably inserted in the base part are attached by means of threaded connectors inserted at the forming side of the mould, because of the dimensions of the base part, and to avoid interference with the networks for air and cooling water. When a mould element has been replaced, the bores for the threaded connectors in the cavity wall have to be shut off or closed and followed by a finishing operation to obtain a desired degree of surface finish.
When finishing the surface of the mould element, a high degree of precision is required. To manipulate the mould element to and from the finishing station, hoisting/manipulating equipment is required. The above mentioned operations require the use of highly skilled man power.